At present, the ink supply devices used on the image printing equipment for supplying a liquid ink, such as large/digital format printers, portrait printers, plotters, etc., fall into two categories: a basket type of ink supply system and a vacuum pump type of ink supply system.
For the basket type, the ink, sucked by an ink pump from the primary (bigger) ink cartridge, is fed through a filter to the secondary ink cartridge, which follows the motion of the jet head and in which the liquid level, 30 mm˜70 mm lower than the jet head position and adjustable, is controlled by an inside level control switch (a float ball).
Advantageously, the basket type of ink supply system is easy in manufacture and low at price with adjustable negative pressure values for each color.
Disadvantageously, the system is incapable of printing materials like plane plates as the small basket has to be lower than the jet head operating platform; not able to clean the jet head rapidly; unstable of the negative pressure value at the jet head surface resulting from a long tube from the secondary ink cartridge to the jet head. Besides, with the carriage under a reciprocate motion, its secondary ink cartridge is apt to leak.
For the vacuum pump type ink supply system, in a position higher than the jet head is arranged the secondary ink cartridge, in which are provided a liquid level switch for liquid level control and a negative pressure sensor for control over air extract from this cartridge by the vacuum pump so as to keep the inside air pressure negative.
Advantageously, the vacuum pump type ink supply system is capable of printing materials in the form of plane plates owing to stable negative pressure values on the jet head surface, and disadvantageously, contains a large numbers of parts and components, the key parts of which have to be imported, its manufacture and test are difficult and expensive. The equipment requires skillful technician trained specially. Besides, it is not easy to adjust negative pressure values for each color or have a rapid jet head cleaning.